| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Auburn | 1 | 14,174 | 13,539 | 0.75% | 1,625 | 9 | City |
| Garrett | 2 | 6,725 | 6,547 | 0.46% | 1,614 | 4 | City |
| Butler | 3 | 2,683 | 2,628 | 0.37% | 1,322 | 2 | City |
| Waterloo | 4 | 2,180 | 2,113 | 0.55% | 1,033 | 2 | Town |
| Ashley | 5 | 1,039 | 1,026 | 0.19% | 546 | 2 | Town |
| St. Joe | 6 | 432 | 412 | 0.7% | 1,290 | 0 | Town |
| Corunna | 7 | 242 | 235 | 0.41% | 1,352 | 0 | Town |
| Altona | 8 | 221 | 214 | 0.45% | 1,089 | 0 | Town |
Auburn is the largest city in DeKalb County, with a population of 14,174.
Altona is the smallest city in DeKalb County, with a population of 221.
There are 8 cities in DeKalb County, Indiana.